From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ira Weiny Subject: Re: [PATCH v5 09/24] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM Date: Fri, 15 Nov 2019 10:06:32 -0800 Message-ID: <20191115180631.GA23832@iweiny-DESK2.sc.intel.com> References: <20191115055340.1825745-1-jhubbard@nvidia.com> <20191115055340.1825745-10-jhubbard@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20191115055340.1825745-10-jhubbard@nvidia.com> Sender: linux-kernel-owner@vger.kernel.org To: John Hubbard Cc: Andrew Morton , Al Viro , Alex Williamson , Benjamin Herrenschmidt , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Christoph Hellwig , Dan Williams , Daniel Vetter , Dave Chinner , David Airlie , "David S . Miller" , Jan Kara , Jason Gunthorpe , Jens Axboe , Jonathan Corbet , =?iso-8859-1?B?Suly9G1l?= Glisse , Magnus Karlsson , Mauro Carvalho Chehab , Michael Ellerman List-Id: dri-devel@lists.freedesktop.org On Thu, Nov 14, 2019 at 09:53:25PM -0800, John Hubbard wrote: > As it says in the updated comment in gup.c: current FOLL_LONGTERM > behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the > FS DAX check requirement on vmas. > > However, the corresponding restriction in get_user_pages_remote() was > slightly stricter than is actually required: it forbade all > FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers > that do not set the "locked" arg. > > Update the code and comments accordingly, and update the VFIO caller > to take advantage of this, fixing a bug as a result: the VFIO caller > is logically a FOLL_LONGTERM user. > > Also, remove an unnessary pair of calls that were releasing and > reacquiring the mmap_sem. There is no need to avoid holding mmap_sem > just in order to call page_to_pfn(). > > Also, move the DAX check ("if a VMA is DAX, don't allow long term > pinning") from the VFIO call site, all the way into the internals > of get_user_pages_remote() and __gup_longterm_locked(). That is: > get_user_pages_remote() calls __gup_longterm_locked(), which in turn > calls check_dax_vmas(). It's lightly explained in the comments as well. > > Thanks to Jason Gunthorpe for pointing out a clean way to fix this, > and to Dan Williams for helping clarify the DAX refactoring. > > Suggested-by: Jason Gunthorpe > Cc: Dan Williams > Cc: Jerome Glisse > Cc: Ira Weiny Reviewed-by: Ira Weiny > Signed-off-by: John Hubbard > --- > drivers/vfio/vfio_iommu_type1.c | 30 +++++------------------------- > mm/gup.c | 27 ++++++++++++++++++++++----- > 2 files changed, 27 insertions(+), 30 deletions(-) > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > index d864277ea16f..c7a111ad9975 100644 > --- a/drivers/vfio/vfio_iommu_type1.c > +++ b/drivers/vfio/vfio_iommu_type1.c > @@ -340,7 +340,6 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, > { > struct page *page[1]; > struct vm_area_struct *vma; > - struct vm_area_struct *vmas[1]; > unsigned int flags = 0; > int ret; > > @@ -348,33 +347,14 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, > flags |= FOLL_WRITE; > > down_read(&mm->mmap_sem); > - if (mm == current->mm) { > - ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page, > - vmas); > - } else { > - ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page, > - vmas, NULL); > - /* > - * The lifetime of a vaddr_get_pfn() page pin is > - * userspace-controlled. In the fs-dax case this could > - * lead to indefinite stalls in filesystem operations. > - * Disallow attempts to pin fs-dax pages via this > - * interface. > - */ > - if (ret > 0 && vma_is_fsdax(vmas[0])) { > - ret = -EOPNOTSUPP; > - put_page(page[0]); > - } > - } > - up_read(&mm->mmap_sem); > - > + ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM, > + page, NULL, NULL); > if (ret == 1) { > *pfn = page_to_pfn(page[0]); > - return 0; > + ret = 0; > + goto done; > } > > - down_read(&mm->mmap_sem); > - > vaddr = untagged_addr(vaddr); > > vma = find_vma_intersection(mm, vaddr, vaddr + 1); > @@ -384,7 +364,7 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, > if (is_invalid_reserved_pfn(*pfn)) > ret = 0; > } > - > +done: > up_read(&mm->mmap_sem); > return ret; > } > diff --git a/mm/gup.c b/mm/gup.c > index b859bd4da4d7..6cf613bfe7dc 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -29,6 +29,13 @@ struct follow_page_context { > unsigned int page_mask; > }; > > +static __always_inline long __gup_longterm_locked(struct task_struct *tsk, > + struct mm_struct *mm, > + unsigned long start, > + unsigned long nr_pages, > + struct page **pages, > + struct vm_area_struct **vmas, > + unsigned int flags); > /* > * Return the compound head page with ref appropriately incremented, > * or NULL if that failed. > @@ -1167,13 +1174,23 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > struct vm_area_struct **vmas, int *locked) > { > /* > - * FIXME: Current FOLL_LONGTERM behavior is incompatible with > + * Parts of FOLL_LONGTERM behavior are incompatible with > * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on > - * vmas. As there are no users of this flag in this call we simply > - * disallow this option for now. > + * vmas. However, this only comes up if locked is set, and there are > + * callers that do request FOLL_LONGTERM, but do not set locked. So, > + * allow what we can. > */ > - if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM)) > - return -EINVAL; > + if (gup_flags & FOLL_LONGTERM) { > + if (WARN_ON_ONCE(locked)) > + return -EINVAL; > + /* > + * This will check the vmas (even if our vmas arg is NULL) > + * and return -ENOTSUPP if DAX isn't allowed in this case: > + */ > + return __gup_longterm_locked(tsk, mm, start, nr_pages, pages, > + vmas, gup_flags | FOLL_TOUCH | > + FOLL_REMOTE); > + } > > return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas, > locked, > -- > 2.24.0 > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9BBD9C33C99 for ; Fri, 15 Nov 2019 18:06:35 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 7EB432073B for ; Fri, 15 Nov 2019 18:06:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7EB432073B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id D8A866EA26; Fri, 15 Nov 2019 18:06:34 +0000 (UTC) Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by gabe.freedesktop.org (Postfix) with ESMTPS id E755C6EA26 for ; Fri, 15 Nov 2019 18:06:33 +0000 (UTC) X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 15 Nov 2019 10:06:33 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.68,309,1569308400"; d="scan'208";a="203454343" Received: from iweiny-desk2.sc.intel.com ([10.3.52.157]) by fmsmga008.fm.intel.com with ESMTP; 15 Nov 2019 10:06:32 -0800 Date: Fri, 15 Nov 2019 10:06:32 -0800 From: Ira Weiny To: John Hubbard Subject: Re: [PATCH v5 09/24] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM Message-ID: <20191115180631.GA23832@iweiny-DESK2.sc.intel.com> References: <20191115055340.1825745-1-jhubbard@nvidia.com> <20191115055340.1825745-10-jhubbard@nvidia.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20191115055340.1825745-10-jhubbard@nvidia.com> User-Agent: Mutt/1.11.1 (2018-12-01) X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Michal Hocko , Jan Kara , kvm@vger.kernel.org, linux-doc@vger.kernel.org, David Airlie , Dave Chinner , dri-devel@lists.freedesktop.org, LKML , linux-mm@kvack.org, Paul Mackerras , linux-kselftest@vger.kernel.org, Shuah Khan , Jonathan Corbet , linux-rdma@vger.kernel.org, Michael Ellerman , Christoph Hellwig , Jason Gunthorpe , Vlastimil Babka , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , linux-media@vger.kernel.org, linux-block@vger.kernel.org, =?iso-8859-1?B?Suly9G1l?= Glisse , Al Viro , Dan Williams , Mauro Carvalho Chehab , bpf@vger.kernel.org, Magnus Karlsson , Jens Axboe , netdev@vger.kernel.org, Alex Williamson , linux-fsdevel@vger.kernel.org, Andrew Morton , linuxppc-dev@lists.ozlabs.org, "David S . Miller" , Mike Kravetz Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Message-ID: <20191115180632.1wskmkbUaUVLYmHc9_2Ahi2MbmI0ffG8sUPiMfei_qk@z> T24gVGh1LCBOb3YgMTQsIDIwMTkgYXQgMDk6NTM6MjVQTSAtMDgwMCwgSm9obiBIdWJiYXJkIHdy b3RlOgo+IEFzIGl0IHNheXMgaW4gdGhlIHVwZGF0ZWQgY29tbWVudCBpbiBndXAuYzogY3VycmVu dCBGT0xMX0xPTkdURVJNCj4gYmVoYXZpb3IgaXMgaW5jb21wYXRpYmxlIHdpdGggRkFVTFRfRkxB R19BTExPV19SRVRSWSBiZWNhdXNlIG9mIHRoZQo+IEZTIERBWCBjaGVjayByZXF1aXJlbWVudCBv biB2bWFzLgo+IAo+IEhvd2V2ZXIsIHRoZSBjb3JyZXNwb25kaW5nIHJlc3RyaWN0aW9uIGluIGdl dF91c2VyX3BhZ2VzX3JlbW90ZSgpIHdhcwo+IHNsaWdodGx5IHN0cmljdGVyIHRoYW4gaXMgYWN0 dWFsbHkgcmVxdWlyZWQ6IGl0IGZvcmJhZGUgYWxsCj4gRk9MTF9MT05HVEVSTSBjYWxsZXJzLCBi dXQgd2UgY2FuIGFjdHVhbGx5IGFsbG93IEZPTExfTE9OR1RFUk0gY2FsbGVycwo+IHRoYXQgZG8g bm90IHNldCB0aGUgImxvY2tlZCIgYXJnLgo+IAo+IFVwZGF0ZSB0aGUgY29kZSBhbmQgY29tbWVu 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